/*
 * Copyright 2025 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.example.nav3recipes.multiplestacks

import androidx.navigation3.runtime.NavKey

/**
 * Handles navigation events (forward and back) by updating the navigation state.
 */
class Navigator(val state: NavigationState){
    fun navigate(route: NavKey){
        if (route in state.backStacks.keys){
            // This is a top level route, just switch to it
            state.topLevelRoute = route
        } else {
            state.backStacks[state.topLevelRoute]?.add(route)
        }
    }

    fun goBack(){
        val currentStack = state.backStacks[state.topLevelRoute] ?:
        error("Stack for ${state.topLevelRoute} not found")
        val currentRoute = currentStack.last()

        // If we're at the base of the current route, go back to the start route stack.
        if (currentRoute == state.topLevelRoute){
            state.topLevelRoute = state.startRoute
        } else {
            currentStack.removeLastOrNull()
        }
    }
}
